Tracking Google Ads Conversions From External Site (Marketplace)
I am new to Google Ads. I am running some Google Ads campaign but I am looking for a way to track conversions.
Unfortunately I cannot use pixel tags because we are selling on a third party site, so we do not have access to it. What I managed to do is set up an event in GA4 for when someone clicks on the “Try it free” button in the marketplace site, and added that as a conversion in Google Ads.
So far so good, but unfortunately there isn’t a sure way to know that someone finished the subscription for the free trial, only that it clicked the button (but then they may have abandoned the process).
I was thinking to create a landing page on our website, with a clickable button to the marketplace, but this is just extra steps, the same problem occuring in this situation also – can’t track who really subscribed for a free trial and who didn’t – just button clicks.
Can’t connect the marketplace to GA4 or Google Ads, as you can do with Shopify or other third parties.
Is there someone with some experience who can guide me in the right direction to accurately track conversions? I am spending money on ads but cannot really track it’s effectiveness. How can I do that? Any ideas? I really appreciate your help. Thanks!
The short answer is:
gclid) from my website to a third-party marketplace? You need a server-side solution to connect the confirmed free trial sign-up data from the marketplace’s backend system back to Google Ads, bypassing the lack of pixel access and the inaccuracy of the button click event.
This involves capturing the Google Click ID (gclid) from the ad click and storing it in your server-side environment or database.
When the actual free trial completion happens on the marketplace, your backend system must retrieve the gclid and use the Google Ads API or the Google Analytics 4 Measurement Protocol to send a definitive, server-to-server conversion event.
The Measurement Protocol is often the most direct path, allowing you to augment your existing GA4 event data with the high-fidelity conversion.
The long answer is:
The core problem is attribution fidelity, where the client-side button click event you’re currently using in Google Analytics 4 (GA4) doesn’t guarantee the server-side subscription conversion.
To accurately track the final conversion, you must implement a server-side data flow leveraging the Google Click ID (gclid), which is automatically appended to your landing page URL by Google Ads.
First, when a user lands on your pre-marketplace landing page, you need to capture the gclid from the URL query parameter and persist it.
Since you cannot drop a conversion pixel on the marketplace, the key is to ensure this gclid travels with the user’s session data until the actual subscription event occurs.
This can be achieved by writing the gclid to a first-party cookie on your domain and then having your server-side system pass this gclid to the marketplace’s sign-up flow, possibly via a unique customer ID in a URL parameter as they are redirected.
Second, your ultimate solution lies in using an API to send the true conversion data.
When the marketplace confirms the free trial subscription and sends a notification or webhook to your backend system, your system must use the stored gclid to initiate a server-side conversion upload.
You have two excellent options: the Google Analytics 4 Measurement Protocol or the Google Ads API.
Using the Measurement Protocol is often the most cost-effective and integrated solution with your existing GA4 setup.
You will construct an HTTP POST request to the GA4 endpoint, sending an event (e.g., free_trial_subscribed) along with the crucial client_id (retrieved from the first-party cookie based on the gclid match) and the gclid itself.
The Measurement Protocol ensures this event is attributed to the correct session and can then be imported into Google Ads as a primary conversion.
This server-side, API-driven approach is cost-effective because it utilizes the Google Analytics 4 Measurement Protocol as a free data pipe, giving you complete control over when and how the conversion is reported.
This bypasses the need for costly third-party tag management on the marketplace, guarantees a reliable, non-browser-restricted conversion signal, and provides a definitive link between your ad spend and the valuable free trial subscription, solving your problem of tracking the ad’s true effectiveness.
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